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Monarch butterflies, which pollinate many different kinds of wildflowers, are among nature’s great wonders. Their annual migration is one of the most awe-inspiring on Earth: Each fall, millions of these striking black-and-orange butterflies take flight on a 3,000-mile journey across the U.S. and Canada to wintering grounds in Mexico’s Sierra Madre mountains.

The Population Plummet

The monarch population, which is determined by measuring the number of hectares the butterflies occupy in their Mexico habitat, has declined to 2.48 hectares—almost 30 percent less than last year’s population. The population has been in steady decline for the past 20 years—reaching a high of more than 20 hectares in 1997 and plunging to 0.67 hectares in 2014. Two decades ago, nearly one billion wintering monarchs blanketed the mountain forests of Mexico. Today, that number has dropped by more than 80 percent.

Herbicides and Milkweed

Heavy use of an herbicide called glyphosate (marketed by Monsanto as Roundup) has greatly diminished milkweed, a native wildflower that is the sole food source for monarch caterpillars and the only plant on which adult monarchs lay their eggs. As milkweed disappears, monarch populations have also plummeted, and the annual migration of monarchs to Mexico is in danger of collapse. And yet the U.S. Environmental Protection Agency (EPA) recently reapproved the registration for Dow’s Enlist Duo, a combination herbicide designed to kill milkweed.

Solutions?

Much effort has gone into planting milkweed throughout the continental U.S. in the past several years in an attempt to make up for the milkweed that has been lost through agricultural practices. Planting milkweed is a great way to help other pollinators, too, as it provides nectar to a diverse suite of bees and butterflies.

But this year’s monarch butterfly population demonstrates that we need to do much, much more if we are going to be successful at building its population back up again to secure numbers. We also need to curb the use of pesticides that are eliminating milkweed in the first place and come up with sustainable solutions—not just for butterflies, but for farmers and our public health.

How NRDC Is Helping Secure a Healthy Future for Monarchs

NRDC envisions a future where monarch populations across North America are healthy and resilient. To achieve this, we’re working at the federal, state, and international levels to secure limits on the use of toxic herbicides and create new milkweed habitat.

We’re taking legal action against against the EPA to win restrictions on toxic herbicides, such as glyphosate, that are killing off native milkweed. And we’re calling on agribusiness companies to withdraw their toxic products. At the state level, we’re working with officials to plant new milkweed habitat along the monarchs’ migration route. Internationally, we’re leveraging pressure by petitioning UNESCO’s World Heritage Committee to upgrade its protection of monarch wintering habitat in Mexico.

Recent NRDC Milestones in the Fight to Save Monarchs

We mobilized more than 113,000 of our members and activists to sign a petition demanding Dow AgroSciences remove Enlist Duo from the market. Not only that, we generated an outcry against Enlist Duo in Congress that included signatures from 32 lawmakers calling on the EPA to take a closer look at the devastating health and environmental impacts of this herbicide.

On the global arena, we ramped up international pressure, including 50,000 petitions from NRDC members and activists, on the UNESCO World Heritage Committee to declare the Monarch Butterfly Biosphere Reserve in Mexico in danger due to the destruction of monarch habitat in the U.S. and Canada by glyphosate. In response, UNESCO launched a formal evaluation of the request.

NRDC and Monarch Watch Planting Milkweed

Monarch Watch is a nonprofit educational outreach program based at the University of Kansas that focuses on the monarch butterfly, its habitat, and its spectacular fall migration. NRDC partners with Monarch Watch to plant milkweed at schools, churches and garden clubs to help save North American monarch butterflies.

Since 2016, Monarch Watch has been distributing milkweed plants, featured in this Monarchs for Moms campaign, for planting on tribal lands and other locations along the monarchs’ migration route.

Monarch butterflies depend on milkweed. They lay their eggs on milkweed, and their caterpillars eat only the leaves of the plant. No milkweed means no monarchs. So the best way to help declining monarch populations—and to preserve their epic, multi-generational migration—is to plant milkweed.

Seems simple, right? But the reality is far more complicated.

Milkweed is slightly toxic—the plant evolved its noxious substances to keep herbivores from chowing down on the leaves. But monarch butterflies evolved tolerance. In fact, they arm themselves with the stuff.

“Monarchs sequester these toxins as an anti-predator defense and anti-parasite defense.”

Louisiana State University biologist Matt Faldyn.

So, by ingesting the toxin, the caterpillars become toxic themselves. That keeps them safe—as long as they don’t ingest too much of the poison. The problem is there are different types of milkweed. And one that’s native to the tropics is now growing in the southern U.S. As these plants sense warming temperatures, they produce more of the toxin—so much more that the monarch butterflies begin to suffer.

To gauge the threat, Faldyn and his team raised monarchs on either the non-native tropical milkweed or on a native milkweed. And they also tested the effects of current environmental conditions as well as temperatures expected for the southern U.S. by the year 2080.

Monarchs that ate native milkweed had comparable survival rates at both current and higher temperatures. But under those future warmer conditions, monarchs raised on the tropical milkweed survived at only one fifth the rate of butterflies raised under current conditions.

The monarchs could thus find themselves in what’s known as an ecological trap. The butterflies seek out milkweed, but what is already the most common type of milkweed in the southern U.S. will eventually kill them.

The tropical species is prettier than the native ones, which is why many people prefer to plant it. But there’s still time to change that.

“What we show is that maybe there should be more of a focus on having native species to your area preferentially planted in your gardens.”

By switching to the native species, home gardeners across the country can each do their part to ensure that monarch butterflies will avoid fluttering their way into the ecological trap—which could be fatal.

ABOUT THE AUTHOR(S)

Jason G. Goldman

Jason G. Goldman is a science journalist based in Los Angeles. He has written about animal behavior, wildlife biology, conservation, and ecology for Scientific American, Los Angeles magazine, The Washington Post, The Guardian, the BBC, Conservation magazine, and elsewhere. He contributes to Scientific American‘s “60-Second Science” podcast, and is co-editor of Science Blogging: The Essential Guide (Yale University Press). He enjoys sharing his wildlife knowledge on television and on the radio, and often speaks to the public about wildlife and science communication.

George and Amy Greer, owners of the Winters-Wall Ranch, are just one of many ranching families enrolled in the Monarch Butterfly Habitat Exchange, which connects landowners along the monarch’s migration route with the resources and scientific expertise they need to become champions of the tiny insect’s recovery.

Other farms and ranches have completed their plans and are awaiting funding from investors like you. The sooner their projects are funded, the sooner they’ll be ready to welcome monarchs home.

Wagley Ranch: Sue and Jay Wagley have nearly 20 years’ experience with habitat restoration. The Exchange is helping them develop a monarch restoration plan focused on implementing prescribed burns that will support growth of native wildflowers, which monarchs need to feed and refuel along their journey.Funding progress:$10,000/$19,985

Elm Ridge Ranch: Less than 1% remains of the native Texas prairie which has long hosted traveling monarchs. The Exchange is helping Elm Ridge Ranch managers adopt a range of conservation activities, including targeted mowing and planting, to turn an old hay field into inviting monarch habitat.Funding progress:$5,600/$15,995

Rust Ranch: Kevin Rust tries to implement at least one project to improve the health of his land each year. This year, the Exchange is helping Kevin contract with a grower who will provide locally harvested milkweed seeds for him to plant monarch habitat this fall.Funding progress:$3,400/$8,505

Shield Ranch: Milkweed is already abundant on this ranch owned by passionate wildlife conservationists, so the Exchange is helping support a plan to enhance the existing habitat with native, monarch-friendly wildflowers and grasses.Funding progress:$12,100/$22,015

Thank you for anything you can give to help make these conservation projects a reality.

The yearly count of monarch butterflies overwintering in Mexico, released Monday, shows a decrease from last year’s count and confirms the iconic orange and black butterfly is still very much at risk. The count of 2.48 hectares of occupied winter habitat is down from 2.91 hectares last winter.

Overall, monarchs have declined by more than 80 percent over the past two decades.

“Another year, another reminder: Our government must do what the law and science demands, and protect monarchs under the Endangered Species Act, before it’s too late,” said George Kimbrell, legal director at the Center for Food Safety. “The remaining question is whether the Trump administration wants to do Monsanto‘s bidding or protect monarchs for future generations.”

“We could lose the monarch butterfly if we don’t take immediate action to rein-in pesticide use and curb global climate change,” said Tierra Curry, a senior scientist at the Center for Biological Diversity and co-author of the 2014 petition to protect monarchs under the ESA.

Roughly 99 percent of all North American monarchs migrate each winter to oyamel fir forests on 12 mountaintops in central Mexico. Scientists estimate the population size by measuring the area of trees turned orange by the clustering butterflies. That population has been dangerously low since 2008. In the mid-1990s the population was estimated at nearly one billion butterflies, but this year’s population is down to approximately 93 million butterflies.

This year’s drop is attributed in part to unseasonal weather last year including late spring freezes that killed milkweed and caterpillars, and an unseasonably warm fall that kept late-season monarchs from migrating.

In 2014 conservationists led by the Center for Biological Diversity and the Center for Food Safety petitioned the U.S. Fish and Wildlife Service (USFWS) to protect the butterfly under the Endangered Species Act. Monarchs are threatened by a host of sources destroying their habitat and food, but studies have shown that a main source of their catastrophic demise decline has been genetically engineered crops, engineered with resistance to Monsanto’s Roundup pesticide, which has dramatically increased the pesticide use on their habitat. The Fish and Wildlife Service’s initial decision was that endangered species protection may be warranted, and pursuant to a court victory the USFWS agreed to make a final decision by June 2019.

A 2016 study by the U.S. Geological Survey concluded that due to ongoing low population levels, there is between an 11 percent and 57 percent risk that the eastern monarch migration could collapse within the next 20 years. Scientists estimate the monarch population needs to reach 225 million butterflies to be out of the danger zone.

Monarchs have lost an estimated 165 million acres of breeding habitat in the U.S. to herbicide spraying and development. The caterpillars only eat milkweed, but the plant has been devastated by increased herbicide spraying in conjunction with corn and soybean crops that have been genetically engineered to tolerate direct spraying with herbicides. In addition to glyphosate, monarchs are threatened by other herbicides including dicamba, Enlist Duo and by neonicotinoid insecticides that are toxic to young caterpillars.

Monarch butterflies west of the Rocky Mountains overwinter on the central coast of California. Their numbers dropped to a five-year low of only 200,000 butterflies this year, down from 1.2 million two decades ago. A recent study found that if current trends continue, the western population has a 63 percent chance of extinction in 20 years and more than an 80 percent chance of extinction within 50 years.